1. Field of the Invention
The present invention is related to electromagnetic radio frequency testing of electronic circuits, and more specifically, to the measurement and testing of radio frequency and electromagnetic interference (EMI) signals in electronic equipment without substantially loading the circuit being measured.
2. Description of the Related Art
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes, thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
Information handling systems such as computers and associated storage disk arrays use high speed data and control buses comprising a plurality of printed-circuit traces or conductors on a printed circuit board (PCB) over which high speed (fast rise and fall time) signals, e.g., electrical pulses, travel between the electronic circuits, e.g., microprocessor, memory, programmable logic array (PLA), application specific integrated circuit (ASIC), serial and parallel interfaces and the like, mounted on the printed circuit board. These electrical pulses are comprised of a plurality of high frequency signals that may generate or be degraded by electromagnetic interference (EMI).
EMI of an information handling system may be measured with a spectrum analyzer for displaying radio frequency spectral energy in the frequency domain, and/or a high frequency oscilloscope for displaying radio frequency spectral energy in the time domain. Some type of radio frequency measurement probe is required in combination with either the spectrum analyzer or oscilloscope. Typical probes that may be used for radio frequency measurement are: current clamp, near field, oscilloscope, and resistive.
The current clamp probe is generally used for measuring radio frequency (RF) alternating current (AC) signals traveling in a cable or wire, and this probe inductively (transformer) couples the RF AC signals in the cable or wire to a radio frequency (RF) spectrum analyzer or oscilloscope. The spectrum analyzer displays RF AC signals in the frequency domain and the oscilloscope displays RF AC signals in the tirne domain. The advantages of this probe are good availability, ease in use, accuracy, isolation between the circuit under test and the test instrument, readily adapted for oscilloscopes and/or spectrum analyzers. A disadvantage of the current clamp probe is that it requires an inductively coupled path (must encircle) with the wire or cable carrying the signal of interest.
The near field probe is a specialized probe that may be used with a RF spectrum analyzer or oscilloscope to measure electric and magnetic fields. Advantages of this probe are availability, ease of use, compatible with oscilloscopes and spectrum analyzers. A disadvantage is that it is only useful in finding the general location of EMI, but it is not precise enough to locate the EMI signal on the circuit, such as a specific signal pin or signal line location.
The oscilloscope probe can measure the RF signal precisely, and can be post processed at the oscilloscope to show frequency (EMI) data, but it is cumbersome to use due to the need for a direct connection to the circuit under test and a nearby connection to a ground reference. The ground lead of the oscilloscope probe can accidentally short circuit to an adjacent circuit and cause catastrophic failures of the circuit under test. It is well known to those having ordinary skill in the art of EMI measurements to use circuit voltage readings on an oscilloscope for determining frequency domain signals. Advantages of the oscilloscope probe are availability and accuracy in calibration with the oscilloscope. Disadvantages are the associated ground connection can short to nearby circuits, and the probe requires an expensive oscilloscope to process the voltage signals in order to determine the frequencies of these signals.
Resistive probes may be used in combination with a RF spectrum analyzer or oscilloscope. The resistive probe is designed to couple the RF signals to the spectrum analyzer or oscilloscope. The resistance probe allows accurate measurements of RF signals, however, it is somewhat cumbersome to use, has the potential of shorting to ground, and is not isolated from the measuring instrument for incidental high voltage contact.
What is needed is a simple, accurate, easy to use and safe probe for measuring radio frequency signals, e.g., EMI, associated with electronic circuits and equipment during testing thereof, preferably does not significantly load the circuit under test so as to affect operation thereof and/or EMI test results.